x86/mce/inject: Only write MCA_MISC when a value has been supplied

x86/mce/inject: Only write MCA_MISC when a value has been supplied

The MCA_MISC register is used to control the MCA thresholding feature on
AMD systems. Therefore, it is not generally part of the error state that
a user would adjust when testing non-thresholding cases.

However, MCA_MISC is unconditionally written even if a user does not
supply a value. The default value of '0' will be used and clobber the
register.

Write the MCA_MISC register only if the user has given a value for it.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240523155641.2805411-2-yazen.ghannam@amd.com